This invention relates to inflatable apparatus for providing support and movement to the lower back.
In the human lower back or lumbar region some degree of lordosis, that is, of forward spinal curvature, is normal. The degree of lordosis varies within the human population, and changes in each person as the back is bent forward (reducing lordosis) or backward (enhancing lordosis). In particular, lordosis is generally less in a person when sitting than when standing, and varies more as a person moves about than when a person is sedentary.
Back pain, and particularly lower back pain, is a widespread and often debilitating malady, occurring intermittently or chronically and ranging in severity from distracting discomfort to agony. Lower back pain may be caused by a disease such as osteoarthritis, an infection, or a tumor; or by a congenital bony defect; or by trauma or injury such as a ruptured intervertebral disk; or by back strain owing to overweight or strenuous work; or even, apparently, by sitting for extended periods. Often the precise cause of lower back pain cannot be satisfactorily determined.
Medical evidence suggests that back pain stems from a complex interplay of personal factors, including the person's age and occupation and the extent to which the person is seated unmoving over the course of the day. Complaints of back pain are increasing among workers having sedentary occupations, and it is well known among occupational health professionals that prolonged static seating places an individual at risk for both acute and cronic back pain associated with muscular, ligamentous, and intervertebral disc problems related to the mechanical stresses of sitting.
Various therapies for lower back pain have been advanced, and these have met with varying degrees of success. Manipulation of the bony elements of the spine by a trained professional therapist is an approach that can provide relief for some kinds of back pain; but often the relief is transitory, and in these cases such an approach can require frequent and repeated visits to the therapist. And, for example, R. McKenzie, 1981, The Lumbar Spine, Spinal Publications Limited, New Zealand, described exercises designed to relieve pain through occasional lumbar movement. The various approaches have not proven adequate to overcome the widespread and persistent problem of back pain associated with sitting.
S. Reinecke et al., 1985, Proc. Am. Soc. Biomechanics, Ann Arbor, Mich., and S. Reinecke et al., 1987, Rehabilitation Engineering Society of North America, 10th Annual Conference, San Jose, Calif., determined tolerance times for static sitting by subjecting persons to static sitting in various positions. Subjects complained of low back pain and indicated that they believed their tolerance times would increase if they were able to move periodically. T. Bendix, 1987, Adjustment of the Seated Work Place, Ph.D. Dissertation, Laegeforeningens Forlag, investigated the effect of movement on seating comfort and postulated that the amount of movement or changes in posture of a seated person can provide a measure of the person's discomfort.
S. Holm et al., 1983, Spine, vol. 8(8), pp. 866-874, studied the effects of various spinal movements on the intervertebral discs of dogs, and concluded that continuous moderate spinal movement for half an hour each day sufficed for maintaining effective nutrition transport to and from disc tissues and for stimulating aerobic metabolism within the most mobile intervertebral discs, of the canine spine. E. Grandjean, 1981, Fitting the Task to the Man, Taylor and Francis, London, suggested that movements that alternately load and unload the spine pump fluid into and out from the discs, improving the nutritional supply to the tissues.
It is known to produce a superficial soft tissue massage effect by means of a plurality of inflatable tubes placed between a person and a seat or mattress. For example, N. Hashimoto et al., U.S. Pat. No. 4,634,179 describes an air lumbar support device for a car seat in which the curvature of the seat back is adjusted by selectively regulating the pressures of a plurality of air bags accommodated in the seat back, including pressure sensors and control means for automatic adjustment to preset pressures. Hashimoto et al. noted that "it may be possible to attain the massage effect of the back and lumbar portions for recovering the fatigue of the driver by means of automatically oscillating the air bag pressures in several kinds of patterns."
T. Kashiwamura et al., U.S. Pat. No. 4,655,505 describes a vehicle seat having embedded in it a plurality of bags to which air is delivered by a compressor through a system of valves. Control means maintain pressure in the bags at preset valves. The pressure may be varied periodically in "a specific air bag for preventing the driver from dozing off." It is also possible "to periodically change the air pressure of all the air bags to the desire of the driver . . . by using a relatively short period or high frequency it is possible to effectively reduce the fatigue of the driver by applying a massage to him."
Alternating pressure pads, sometimes termed "ripple" pads, have interdigitating sets of tubes or cells that are alternately or serially inflated and deflated so that the person is supported by pressure at different areas of -the body at different times, to produce a superficial soft tissue massage effect. Some of these include a timed cycle of inflation together with pressure control or pressure regulation, as described for example in A. E. Corbett et al., U.S. Pat. No. 4,255,989, R. J. P. Evans, U.S. Pat. No. 3,678,520, J. A. Green, U.S. Pat. No. 4,132,228, W. C. Morrell, U.S. Pat. No. 3,867,732, and R. J. D. Welch, U.S. Pat. No. 4,193,149.